Darwin used a few examples in his writings such as animals changing to their environment, physical characteristics, and even losing organs that offer no help to the creature anymore. (Teeth for example that disuse with time, as the mature creature doesn’t use them, or has no reason for them. These changes take time and cannot be accurately measured within a single life time. As he wrote: “It cannot be pretended that we know all the varied means of distribution during the klong lapse of years…” He also brings up the topic of variability. Variability is a lack of consistency or tends to vary, which is a very simplified example of gene mutations. He says it’s hard to judge how an animal evolves, but it has to do with the use of parts, environment, and how well an animal survives. If one creature has a sought-after trait that gives it an advantage, it’s likely that the creature will pass on its genes to future generations. Through variability, some of its offspring might have the same mutation that give them a better chance of survival. The cycle continues until most of the population has the now, common gene.
I think what made me think the most was having him, give an example of not necessarily a species, but the idea and how a certain change could inherently help the individual. I connected this to my past knowledge of human evolution and how a larger brain and the ability to work in large groups gave early humans a huge advantage over other animals. The better you play with others, the more likely you would have others looking out for your well-being.